☆ 4.3 Review

Approaches of estrous synchronization in sheep: developments during the last two decades: a review

TROPICAL ANIMAL HEALTH AND PRODUCTION (2021)

Journal

TROPICAL ANIMAL HEALTH AND PRODUCTION

Volume 53, Issue 5, Pages -

Publisher

SPRINGER

DOI: 10.1007/s11250-021-02932-8

Keywords

Estrus synchronization; Progesterone; eCG; Ram effect; Prostaglandins

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Abstract

This review summarizes the protocols used for estrous synchronization in ewes over the past two decades, highlighting the use of progesterone as a major hormone along with gonadotropins and prostaglandins. The supplementation of P4-based protocols with eCG improves fertility, while the ram effect can be an alternative.

The objective of the current review was to summarize the protocols used for estrous synchronization in ewes during the last two decades. Progesterone (P4) is a major hormone used in most protocols. P4 in the form of a controlled internal drug releasing (CIDR) device, medroxyprogesterone acetate (MAP), and fluorogestone acetates (FGA) has been used for estrous synchronization. Also, gonadotropins such as equine chorionic gonadotropin (eCG) and gonadotropin-releasing hormone (GnRH) are often administered at the end of P4-based protocols to improve fertility. Moreover, the administration of prostaglandins (PG) and ram effects have been used for estrus induction and synchronization of ewes. The findings of previous studies indicate that the outcome of administering various synthetics P4 analogues (CIDR, MAP, and FGA) in ewes is comparable in terms of estrous synchronization/induction. The supplementation of P4-based protocols with eCG, however, improves the estrus response and pregnancy rate during breeding and non-breeding season. On the other hand, PG is effective for successful estrous synchronization during the breeding season only. Often, two injections of PG are administered either 11 or 14 days apart along with P4-based protocols to lyre ovine corpus luteum (CL) when it is receptive to PG i.e., 3 days post-ovulation. Alternatively, the ram effect has been shown to improve the efficacy of P4-based protocols and can be used as an alternative to eCG in ewes. The current review describes the methods of synchronization and their outcomes during breeding and a non-breeding season in ewes.

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Comparison of Gonadotropin-Releasing Hormone versus Estrogen-Based Fixed-Time Artificial Insemination Protocols in Grazing Bos taurus Suckled Beef Cows

Luis B. Ferre, Julian Jaeschke, Juliana Gatti, Gerardo Baladon, Ezequiel Bellocq, Gustavo Fernandez, Ramiro Rearte, Michael E. Kjelland, Marcos G. Colazo, Jordan M. Thomas

Summary: The study aimed to determine whether Gonadotropin-releasing hormone (GnRH)-based protocols can replace estrogen-based protocols in fixed-timed artificial insemination (FTAI) for grazing Bos taurus suckling beef cows in South America. The results showed that GnRH-based protocols outperformed estrogen-based protocols in terms of plasma progesterone concentrations, percentage of cows with a corpus luteum, and pregnancy per artificial insemination (P/AI). The 7 & 7 GnRH protocol achieved the highest P/AI.

ANIMALS (2023)